Mechanical Ventilation Systems. Mechanical ventilation systems can be useful tools for improving indoor air quality in tightly built homes, but they must be regularly operated in order to be effective. The results of a study done for Canada's Department of Energy, Mines, and Resources suggests that homeowners use these systems less frequently than they should, however. The study monitored the use of 17 ventilation systems installed in tight homes. According to the study, central exhaust ventilation systems were used only about 37 minutes per day, achieving an average of only .01 air changes per hour (ACH), or 3% of installed capacity. Those heat recovery ventilation systems tested, even though designed for continuous operation (unplugging these systems is the only way to turn them off), were used only about 19.3 hours per day, achieving an average of .33 ACH. The study also found that the type of system affected how it was used, and that many homeowners participating in the study did not understand how to operate their ventilation system. Researchers concluded that more attention should be given to operation and control of the systems, and to homeowner education. See a related article in this Home Energy Integrated Heating and Ventilation: Double Duty for Ducts. (Solplan Review, August/September 1992)

Residential Air Cleaners. Airborne particles in the indoor environment such as radon, tobacco smoke, fibers, and microbiological matter can be harmful to human health. There are a variety of air cleaners available today to reduce these pollutants. Three California researchers--Richard Sextro from Lawrence Berkeley Laboratory, and Francis Offermann III and Steven Loiselle, both from Indoor Environmental Engineering in San Francisco--studied six air cleaners used in conjunction with residential forced-air heating and cooling systems to determine their effectiveness at reducing indoor particles. The study assessed two panel filters (a standard disposable furnace filter and a reusable passive electrostatic filter), two air-surface filters (a bag filter and a high-efficiency particle arrester, or HEPA), and two electrostatic precipitators (a flat plate and a foam pad). Tests were conducted in the Indoor Air Quality Research House, which has an infiltration rate of about .1 air change per hour (ACH). Test results showed that panel filters are least effective, removing about the same level of particles as air circulation, without a filter (9%). The most effective devices were the bag filter (reducing particles by 80.6%), electrostatic precipitators (76% particle reduction), and HEPA filter (75% particle reduction). The study also concluded that while these devices can reduce indoor particles, they do not eliminate the need for effective ventilation. (ASHRAE Journal, July 1992)

Designs to Control Attic Moisture. According to Swedish researcher Ingemar Samuelson, moisture-laden indoor air is the second leading cause of attic moisture (rain leakage is first). Since Swedish homes are built especially tight, their attics remain very cold, and any moisture that finds its way into the attic is likely to condense, which can ultimately lead to problems. The condensate freezes and accumulates. Ceilings are known to collapse under the weight. Samuelson tested two new designs aimed at controlling attic moisture, and found both slightly effective. The first design included a thin layer of rigid foam insulation applied underneath roof sheathing. In the second design, similar insulation was applied to the roof and attic ventilation was also eliminated. Field tests showed that attics with one inch of foam insulation applied to roof sheathing and no outside ventilation were 5-8% drier and 1-2deg.F warmer than conventional attics. Samuelson warns, however, that eliminating attic ventilation poses risks. Additionally, the study did not consider how roof insulation would affect the temperature or durability of shingles. (Energy Design Update, December 1992)

Pellet Air Conditioner. A new air conditioning system fueled with wood pellets can save as much as 35% in fuels costs over its electricity-driven counterpart. The system was developed by Balo Thermotech, of Fresno, California, and is intended for homes and small businesses. Though the basis for comparison isn't clear, a 5-ton prototype tested in an 1,800 ft2 office building is reported to have performed better than a 7.5 ton electric unit, consuming about 2.5-5.5 lbs of fuel per hour (dispensed from a bin), depending on outside temperature. In addition to cooling, the system is capable of providing space heat during the winter. As an added bonus, the thermostatically controlled system uses an ammonia absorption refrigeration cycle, rather than conventional chlorofluorocarbon or hydrochlorofluorocarbon refrigerants. (Fiber Fuels Institute Newsletter, September/October 1992)